Donate and Help Conservation Research?

[ConservationTech]

Hi There,

I am a Conservation Technician who works with Conservators at the Smithsonian Institution.

For several years, we have been studying a hologram. This hologram, we believe to be a white-light-illuminated reflection type (Denisyuk type) hologram comprised of Silver Halide Gelatin (SHG) image forming emulsion on a glass support adhered to a black mount.

We are curious to experiment with damage and repair on test material. I am writing now, to request that test material. These experiments could be shared in a forthcoming presentation at the American Institute for Conservation conference this summer.

We would make sure to preform photodocumention on the object before and after experimentation. Again, experimentation means damaging the hologram, intentionally. We would make sure to share the artist's name and credit them in our presentation.

Q: Given the above, Would anyone be interested in donating a glass white-light reflection hologram? Unbacked/transparent mount, wherein the emulsion is directly on glass?

[jrburns47]

Do you know the manufacturer and specific emulsion type of the plate you’ve been testing?
Apparently similar work has been going on at NorthWestern as well.

[jrburns47]

As you no doubt know, there are a lot of variables that go into conserving these types of holograms recorded in silver halide emulsions. They would include, but not limited to, manufacturer, lot or batch #, various post exposure darkroom processing regimes including water wash steps, subsequent exposure to heat, humidity and light, etc.

[BobH]

Please contact me directly at the address below. I have plates like you describe that I can send to you that are from 1965, and experience with holograms from the 1960s. I'm also very curious about the hologram you have. Also, please visit my site also mentioned below.

laserhistorymuseum.com
bob@laserhistorymuseum.com

[Joe Farina]

Hi,

I think this would be a very interesting area of research. As far as I know, there has never been an independent and unbiased evaluation of the permanence or longevity of holograms. Holograms vary enormously in terms of recording material, processing regime, sealing or mounting technique, and type of storage conditions they are subjected to.

About 30 years ago I did the following hologram on bleached silver halide material. This is a simple Denisyuk hologram on Agfa 8E75 film. The back of the film was sprayed with black paint. I cannot see any fading/dimming/deterioration, but this hologram has been stored in darkness for the last 30 years. (The object is a cylinder seal impression from the British Museum, BM 116149). I can donate a few of these if you like.

Since you are looking for unbacked (unpainted) silver halide emulsion on glass (which I don't currently have), I would be happy to look for one, and donate it for research. Or, if a forum member has one, I can recompense the forum member then donate it.

For a typical silver halide hologram, I think longevity tests based on light exposure over time will prove disappointing. There are too many variables involved in processing, and bleached silver halide crystals are not very forgiving in terms of light-stability over time. After all, bleached (transparent) silver halide crystals are essentially the same thing as "unexposed" silver halide crystals, which are, of course, light sensitive.

On the other hand, there is a processing technique called "colloidal" silver where the crystals are converted back to pure metallic silver. This appears to be a much more stable situation. This technique was used extensively in Russia.

Another type of recording material which is very popular at the moment is photopolymer, specifically Bayfol HX200. This is a very easy to use material which is sensitive to blue, green, and red light, thus enabling full-color holograms. It doesn't require any wet processing at all, just post-exposure UV light. As far as I know, no independent evaluation has been made regarding the stability of finished Bayfol holograms over time.

After 35 years of working with holography, I have settled on DCG (dichromated gelatin) as the most likely material to stand the test of time. Many people criticize DCG holograms because they can vanish on exposure to high humidity. This only happens when the hologram is sealed improperly. If the hologram is sealed, following correct procedures with an archival epoxy (the material called Hxtal, which was developed for conservation), I am convinced that the hologram will last indefinitely. The image-forming components of the hologram are only gelatin and air. The correct sealing procedures do involve a certain amount of care, including degassing of the epoxy with a vacuum pump, and preparation of the glass surfaces with silane. But once the protocols have been correctly worked out, the actual procedure is not difficult at all.

[Din]

Hi,

I think this would be a very interesting area of research. As far as I know, there has never been an independent and unbiased evaluation of the permanence or longevity of holograms.

http://resources.culturalheritage.org/p ... 5_Wise.pdf

[Joe Farina]

Thanks, Din, this paper is new to me, and I appreciate it.

The paper is disappointing, because it's more of a "survey" of art, rather than a technical study. It did have an interesting list of potential problems with silver halide materials. I think this might be useful for the original poster.

[Din]

Thanks, Din, this paper is new to me, and I appreciate it.

The paper is disappointing, because it's more of a "survey" of art, rather than a technical study. It did have an interesting list of potential problems with silver halide materials. I think this might be useful for the original poster.

I've had many a conversation about conservation of holography with Edwina Orr, Jody Burns, Stephen Hart and others. The point I felt that display holographers didn't see was that the method of image production is different from that of a photograph. In photographs, the image is produced by a grey scale variation in the oxidation of the silver based on the grey scale variation of the focused image, while in holography, there is no grey scale, but (ideally) a sinusoidal profile. Therefore the plane (fringe) structure of the hologram was quite important. In technical holography, the plane (fringe) structure is vital to achieve the optical function and whenever I designed a hologram, I was always studied and designed around the desired planar structure. In display holography, the spatial frequency of the planes (fringes) is a factor that does not exist in a photograph and is important, because any decay in the spatial structure will cause aberrations, while any decay of the grey scale in a photograph will not cause aberrations but intensity variations - a photographic image may fade, for example, but not distort or colour shift, over time.

There were interesting points in the paper:

" Holograms do have many physical similarities to photographs and so comparable
considerations can apply"
I'm not sure I agree here, as I've described above

"Accelerated ageing indicated that there was a change in silver particle morphology
and that hologram deterioration was largely catalysed by residual processing chemicals,
accentuated by the small developed grain size in the image silver, resulting in a loss of resolution."
Agree. Stephen Hart used accelerated ageing methods and found a similar result.

"However, it has been suggested, that long term exposure to light can also cause this shift from red to blue, and that this
change can be irreversible, as a result of permanent shrinkage of the gelatin in the emulsion layer.
(Orr, 2012)"
This is presumably Edwina Orr and David Trayner (who, by the way, were my mentors in 1982 along with Peter Miller). I have thought about this, but i couldn't see a straightforward mechanism. One possibility is that light causes hardening and so causes shrinkage, and one way I thought of testing this theory was to record a hologram on just gelatin - no photo-receptors. Of course it needs to be a great deal of light. We (Joy and I) did coat glass with just gelatin and hoped to have Ron Olson record a hologram with a pulse. Unfortunately I never contacted Ron and nothing came of it. So, reading this statement by Edwina, she must have tried exposing a hologram to light and seen a blueshift

Heat is particularly a problem for holograms with a black backing, so lighting of negligible heat as well as UV emission
should be chosen.
This is a statement by Hans Bjelkhagen and I agree up to a point. But, we (Joy and I again) did carry out accelerated ageing under several scenarios and we found that ageing occurred more rapidly with UV than with any other accelerated ageing method. So, UV is more important than heat. The answer is, of course, obvious, since AgBr is particular sensitive to UV (I believe the sensitivity peaks at around 300nm)

I talked to Joy this morning about the spatial frequency issue, and she brought out another point. The original conservator says the original artist would be recognised. But, several of these older holograms are in collections and not owned by the actual artists. Also, older holograms were never "signed", in that very few know who the actual artists were. There was an exhibition of holograms at the Museum of Contemporary Art (MOCA) in Los Angeles, and it was disappointing that none of the holograms on display had the artist's name displayed.

[ConservationTech]

Do you know the manufacturer and specific emulsion type of the plate you’ve been testing?
Apparently similar work has been going on at NorthWestern as well.

Thank you, Jrburns47, for directing me to the work at Northwestern. Has anyone seen papers come out of this Northwestern project besides the one on NeRF? Linked below.

https://www.mccormick.northwestern.edu/ ... h-nerf.pdf

In talking with another holographer over the last few weeks, we think our hologram, given its dims @ 15 3/4 × 11 1/2 in. (40 × 29.2 cm) and its make in 1983, we think it may be an AGFA plate? Thoughts?

Tess

[ConservationTech]

Hi,

I think this would be a very interesting area of research. As far as I know, there has never been an independent and unbiased evaluation of the permanence or longevity of holograms. Holograms vary enormously in terms of recording material, processing regime, sealing or mounting technique, and type of storage conditions they are subjected to.

About 30 years ago I did the following hologram on bleached silver halide material. This is a simple Denisyuk hologram on Agfa 8E75 film. The back of the film was sprayed with black paint. I cannot see any fading/dimming/deterioration, but this hologram has been stored in darkness for the last 30 years. (The object is a cylinder seal impression from the British Museum, BM 116149). I can donate a few of these if you like.

Since you are looking for unbacked (unpainted) silver halide emulsion on glass (which I don't currently have), I would be happy to look for one, and donate it for research. Or, if a forum member has one, I can recompense the forum member then donate it.

For a typical silver halide hologram, I think longevity tests based on light exposure over time will prove disappointing. There are too many variables involved in processing, and bleached silver halide crystals are not very forgiving in terms of light-stability over time. After all, bleached (transparent) silver halide crystals are essentially the same thing as "unexposed" silver halide crystals, which are, of course, light sensitive.

On the other hand, there is a processing technique called "colloidal" silver where the crystals are converted back to pure metallic silver. This appears to be a much more stable situation. This technique was used extensively in Russia.

Another type of recording material which is very popular at the moment is photopolymer, specifically Bayfol HX200. This is a very easy to use material which is sensitive to blue, green, and red light, thus enabling full-color holograms. It doesn't require any wet processing at all, just post-exposure UV light. As far as I know, no independent evaluation has been made regarding the stability of finished Bayfol holograms over time.

After 35 years of working with holography, I have settled on DCG (dichromated gelatin) as the most likely material to stand the test of time. Many people criticize DCG holograms because they can vanish on exposure to high humidity. This only happens when the hologram is sealed improperly. If the hologram is sealed, following correct procedures with an archival epoxy (the material called Hxtal, which was developed for conservation), I am convinced that the hologram will last indefinitely. The image-forming components of the hologram are only gelatin and air. The correct sealing procedures do involve a certain amount of care, including degassing of the epoxy with a vacuum pump, and preparation of the glass surfaces with silane. But once the protocols have been correctly worked out, the actual procedure is not difficult at all.

Thank you, Joe Farina, for this thoughtful reply. I will message you privately about possible donations.

Tell me -- What kind black spray paint? Enamel/acrylic? Any preference?

It is interesting to hear your take on DCG stability. And your thoughts on SHG light exposure.

Any thoughts on SHGs that are black backed? Heat conductivity and absorption of light? Any display recommendations for white-light reconstruction? Light sources that don't exacerbate heat and lux exposure? Colored filters on lights OR LED alternatives?